This invention relates to a novel family of metallophosphates, collectively designated AlPO-78. They are represented by the empirical formula:R+rMm2+EPxSiyOz where M is a divalent framework metal such as magnesium or zinc, R is an organoammonium cation, and E is a trivalent framework element such as aluminum or gallium.
Classes of molecular sieves include crystalline aluminophosphate, silicoaluminophosphate, or metalloaluminophosphate compositions which are microporous and which are formed from corner sharing AlO4/2 and PO4/2 tetrahedra. In 1982, Wilson et al. first reported aluminophosphate molecular sieves, the so-called AlPOs, which are microporous materials that have many of the same properties as zeolites, although they do not contain silica (see U.S. Pat. No. 4,310,440). Subsequently, charge was introduced to the neutral aluminophosphate frameworks via the substitution of SIO4/2 tetrahedra for PO4/2+ tetrahedra to produce the SAPO molecular sieves as described by Lok et al. (see U.S. Pat. No. 4,440,871). Another way to introduce framework charge to neutral aluminophosphates is to substitute [Me2+O4/2]2− tetrahedra for AlO4/2− tetrahedra, which yields the MeAPO molecular sieves (see U.S. Pat. No. 4,567,029). It is furthermore possible to introduce framework charge on AlPO-based molecular sieves via the simultaneous introduction of SiO4/2 and [M2+O4/2]2− tetrahedra to the framework, giving MeAPSO molecular sieves (see U.S. Pat. No. 4,973,785).
Numerous molecular sieves, both naturally occurring and synthetically prepared, are used in various industrial processes. Synthetically, these molecular sieves are prepared via hydrothermal synthesis employing suitable sources of Si, Al, P, metals, and structure directing agents such as amines or organoammonium cations. The structure directing agents reside in the pores of the molecular sieve and are largely responsible for the particular structure that is ultimately formed. These species may balance the framework charge associated with silicon or other metals such as Zn or Mg in the aluminophosphate compositions, and can also serve as space fillers to stabilize the tetrahedral framework. Molecular sieves are characterized by having pore openings of uniform dimensions, having a significant ion exchange capacity, and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent molecular sieve crystal structure. Molecular sieves can be used as catalysts for hydrocarbon conversion reactions, which can take place on outside surfaces as well as on internal surfaces within the pore.
As stated above, molecular sieves are capable of reversibly adsorbing and desorbing certain molecules depending on the adsorbate's size and the molecular sieve's internal pore structure. There are many applications where it is desired to adsorb water vapor, preferably in a reversible manner. One such application is an adsorption heat pump, which is a device that can be used to recover energy from exhaust or waste heat. As such, adsorption heat pumps can be utilized to maximize energy efficiency in an environmentally friendly manner. Molecular sieves can be useful materials to act as water vapor adsorbents in an adsorption heat pump due to their high capacity for water vapor. A description of the use of adsorbents in adsorption heat pumps can be found in U.S. Pat. No. 8,323,747, incorporated by reference herein in its entirety.
The type of molecular sieves used in adsorption heat pumps must meet certain requirements for optimal performance. A high overall capacity for water vapor is important, but most critically, they should fully desorb all adsorbed water at no greater than 100° C. Otherwise, too much heat must be applied to fully remove the adsorbed water from the micropores (i.e., the regeneration temperature is too high), thus requiring too high of an energy input. The majority of aluminosilicates (i.e., zeolites) have rapid uptake of water vapor at very low pressures (P/P0), which conversely leads to an unacceptably high regeneration temperature, despite a high overall capacity for water vapor. Aluminophosphates and silicoaluminophosphates have been shown to have more favorable adsorption characteristics for water vapor (see, for example, M. F. de Lange et al. CHEM. REV. 115, 12205 (2015); H. van Heyden et al. APPL. THERM. ENG. 29, 1514 (2009). In particular, the materials SAPO-34 and SAPO-5 (zeotypes CHA and AFI, respectively) have been shown to have particular utility as adsorbent materials in adsorption heat pumps (see U.S. Pat. Nos. 7,422,993 and 9,517,942).